1. Field of the Invention
This invention relates to a method for surface treating a chemically inert molded article of a fluorinated olefin polymer.
2. Description of the Prior Art
Molded articles of fluorinated olefin polymers, such as films, sheets, tapes or cloths, are widely used because of their superior properties such as electrical characteristics, thermal characteristics and chemical resistance, but they have the defect that since their surface is inert, they exhibit low adhesion so good adherance of adhesives, paints, inks, etc., is hard to obtain and composites with other materials are difficult to obtain.
In conventional techniques, the surface of such a molded article is treated, for example, by a physical roughening of the surface, or by glow discharge. Such a physical surface treatment, however, scarcely improves the surface of a molded product of a fluorinated olefin polymer typified by a polytetrafluorethylene molded article. Furthermore, by a glow discharge, the degree of improvement of the surface of the molded article is far inferior to that of a fluorine-free polymer such as polyethylene.
When it is desired to obtain a strongly adhesive surface, the only treatment method now commercially available is one comprising immersing a fluorinated olefin molded article into a solution of an alkali metal such as metallic sodium in a mixture of naphthalene and tetrahydrofuran or in liquid ammonia. However, in this method the alkali metal used creates the risk of fire during treatment, and handling of the used treating liquor also poses problems. Furthermore, since the treated surface of the molded article turns brown, its commercial value is lowered, and its surface electrical resistance is reduced. Another defect is that the treating effect (surface adhesion) is drastically reduced when the treated surface of the molded article is exposed to ultraviolet light or left to stand at elevated temperatures.